Road vehicles, in particular heavy goods vehicles and rail vehicles, are often equipped with a compressed air supply system, by which compressed-air-consuming circuits, such as service brake circuits, a handbrake circuit, an air suspension circuit, a leveling adjustment circuit or auxiliary consumer circuits are supplied with compressed air. In order to adjust the working pressure of compressed-air consumers, control valves comprising at least one control piston guided in an axially movable manner in a cylinder fixed to the housing are frequently used. The control piston, which is sealed by at least one sealing ring arranged on the outer circumference of the control piston, separates two pressure chambers from one another. One of the pressure chambers is conventionally a working pressure chamber, which is connected to a working pressure connection of a consumer and, depending on the axial position of the control piston, can be connected to a supply pressure connection or to a vent outlet or shut off from both. The other pressure chamber can be a control pressure chamber or an equalizing chamber connected to the surroundings by a vent hole. The control piston can be displaced mechanically, pneumatically or electromagnetically to adjust the axial position thereof. In a compressed-air brake system of a vehicle, a control valve of this type incorporated in a piston design can be used as a motor vehicle brake valve, as a trailer control valve, as a trailer brake valve or as a relay valve.
DE 101 20 321 B4 discloses a relay valve of a compressed-air brake system, comprising a pneumatically displaceable control piston, in which the control piston is guided in an axially movable manner in a cylinder of a valve housing and separates a working pressure chamber from a control pressure chamber. The control pressure chamber can alternately have a control pressure applied thereto or can be switched so as to be unpressurized by a magnetic valve. To seal the control piston, a radial sealing ring comprising a fastening web in the form of an outer annular web is inserted in a fastening groove in the form of an annular groove in the inner wall of the cylinder, and the piston is provided with a correspondingly long, cylindrical outer wall acting as a sealing surface.
DE 10 2009 040 759 A1 describes an additional relay valve of a compressed-air brake system, comprising a pneumatically displaceable control piston, in which the control piston is guided in an axially movable manner in a cylinder of a valve housing and separates a working pressure chamber from a control pressure chamber. The control pressure chamber can alternately have a control pressure applied thereto or can be switched so as to be unpressurized by a pilot valve, which is not described in greater detail. To seal the control piston, an O-ring is inserted in an annular groove formed in the cylindrical outer wall of the control piston. For the axial guidance thereof, the control piston is mounted by a relatively long, central mounting pin so as to slide in a central mounting hole of a housing cover.
A similar relay valve of a compressed-air brake system comprising a pneumatically displaceable control piston is also known from DE 10 2014 009 179 A1. The control piston is guided in an axially movable manner in a cylinder of a valve housing and in this case as well separates a working pressure chamber from a control pressure chamber. To seal the control piston, a sealing ring having a Z-shaped profile is inserted in an annular groove formed in the cylindrical outer wall of the control piston. For the axial guidance thereof, the control piston is mounted so as to slide via a central guide sleeve on a mounting pin fixed to the housing.
As a result of the sliding guidance thereof by a central guide sleeve or a central mounting pin, the control pistons of the known control valves each have a disadvantageously great axial height, by which in particular the axial dimensions of the relevant control valve are increased. In addition, the sealing of the pressure chambers separated by the control piston by only one respective sealing ring arranged on the outer circumference of the control piston is designed to be relatively weak in the two last-mentioned embodiments of the known control valves.